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This N of 1 study utilizes a withdrawal design with aggressive responses of a 27-year-old male exhibiting autistic behavior. The frequency of physical and verbal aggressive responses was decreased by reinforcing attempts to relax (utilizing EMG biofeedback) when discriminative stimuli for aggressive behavior were present.
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Multiunit activity was chronically recorded in the hippocampus (CA3 field), the magnocellular medial geniculate (MGm) and the auditory cortex (AC) of rats during acquisition (12 daily sessions, 10 trials per session) and long-term retention of differential classical conditioning (tones paired with footshocks). Marked increases of multiunit discharges to CS + presentations were first detected in the MGm (5-10 trials) followed (10-20 trials) by the emergence of discriminative responses in the hippocampus and in the AC. During long-term retention tests, 45 days after the end of conditioning, CS + selective responses were observed in the 3 structures. We propose that learning-induced changes in the conditioned stimulus (CS) sensory pathway can have the same temporal stability as the sensory plasticity observed during development or post injury in adult animals.
Single auditory cortical neurons express their sensitivity to the amplitude of a preferred-frequency tone pulse as either a monotonic, saturating intensity profile or as a non-monotonic, bell-shaped intensity function. In the presence of continuous, wideband noise masking, the tone intensity profile is displaced toward higher tone levels. The magnitude of the tone threshold adjustments brought about by increments in noise level very closely match the elevations in noise amplitude. The mechanisms underlying the threshold adjustments likely include neural adaptation. This is because the tone threshold shifts seen in the spike count data are paralleled by spike latency data, and because recovery of tonal sensitivity following noise offset proceeds in a negatively-accelerating fashion. In some instances, the slope of the masked tone intensity profile is greater than that for unmasked tones. For masked tone levels evoking submaximal responses, this has the consequence that cortical responses to masked tones are somewhat more salient than those for unmasked tones of comparable suprathreshold level. These observations bolster our understanding of the psychophysics of noise-masking in normal listeners, and they provide a partial explanation of the difficulty shown by patients with temporal lobe lesions in discriminating signals in noise.
Two same/different discrimination tasks were performed by amateur-musician subjects in this functional magnetic resonance imaging study: Melody Discrimination and Harmony Discrimination. Both tasks led to activations not only in classic working memory areas--such as the cingulate gyrus and dorsolateral prefrontal cortex--but in a series of premotor areas involved in vocal-motor planning and production, namely the somatotopic mouth region of the primary and lateral premotor cortices, Broca's area, the supplementary motor area, and the anterior insula. A perceptual control task involving passive listening alone to monophonic melodies led to activations exclusively in temporal-lobe auditory areas. These results show that, compared to passive listening tasks, discrimination tasks elicit activation in vocal-motor planning areas.
The perception of pure tone sequences in highly dependent on the serial pattern of tone frequencies. We propose that this phenomenon is mediated by a frequency-selective mechanism. Three models of the selective mechanism were evaluated in a temporal discrimination task. The observer was required to discriminate between two sequences of tone bursts. In one sequence the time interval between each tone burst was constant; in the other sequence the time interval was a random variable. A set of fixed and random pattern rules determined the frequency of each tone in the sequence. Discrimination performance was studied as a function of the magnitude of the time interval jitter and the serial pattern of tone frequency. Performance in the fixed pattern conditions was well described by a multiple-channel model in which timing information is available between tones within the same frequency region. The influence of higher order attentional factors was randomly determined. The frequency-selective mechanism appears to be sensitive to uncertainty about the frequency pattern of the input. Repeating the random pattern within each trial effectively eliminated this uncertainty. This result is consistent with experiments on the discrimination of word-length auditory patterns and temporal cues in speech.
The present study was designed to investigate the effect of stimulus frequency on the ability to discriminate the temporal sequence of two 250 ms-duration dichotic stimuli. Dichotic stimulus pairs of three frequencies were tested, 493 Hz, 988 Hz and 3982 Hz, using a three-alternative forced-choice design. The results indicate that frequency does not affect the form, the slope or the location along the abscissa of the discrimination functions. All functions reached 67% discrimination level with a dichotic temporal asymmetry of approximately 40-45 ms.
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Past research has shown a superiority of participants with high-functioning autism over comparison groups in memorizing picture-pitch associations and in detecting pitch changes in melodies. A subset of individuals with autism, known as "musical savants," is also known to possess absolute pitch. This superiority might be due to an abnormally high sensitivity to fine-grained pitch differences in sounds. To test this hypothesis, psychoacoustic tasks were devised so as to use a signal detection methodology. Participants were all musically untrained and were divided into a group of 12 high-functioning individuals with autism and a group of 12 normally developing individuals. Their task was to judge the pitch of pure tones in a "same-different" discrimination task and in a "high-low" categorization task. In both tasks, the obtained psychometric functions revealed higher pitch sensitivity for subjects with autism, with a more pronounced advantage over control participants in the categorization task. These findings confirm that pitch processing is enhanced in "high-functioning" autism. Superior performance in pitch discrimination and categorization extends previous findings of enhanced visual performance to the auditory domain. Thus, and as predicted by the enhanced perceptual functioning model for peaks of ability in autism (Mottron & Burack, 2001), autistic individuals outperform typically developing population in a variety of low-level perceptual tasks.
To test the hypothesis that prior patterned or varied auditory experience was necessary for the development of discrimination of auditory frequency, Sprague-Dawley albino rats were deprived of patterned sound from birth by the technique of rearing them in white noise. The sound-deprived rats learned a frequency discrimination as easily as controls reared in varied sound conditions.
The Kamin blocking phenomenon occurs when behavioral expression of conditioning to a novel stimulus fails in the presence of a previously conditioned stimulus (CS). Neural metabolic effects of a tone conditioned as an excitor were compared to the effects of the same physical tone when excitatory conditioning was blocked by previous conditioning with a light. We examined the metabolic activity of the auditory system to test the hypothesis that auditory processing of a tone CS changes during blocking. Quantitative histochemistry of cytochrome oxidase (C.O.), the final mitochondrial enzyme for oxidative metabolism, was used to evaluate cumulative changes in the metabolic capacity of the auditory system resulting from blocking. Rats (Long-Evans) in the Blocking group received pairings of a light CS with a mild footshock unconditioned stimulus (US) during Phase 1 training. Rats in the Control group received random presentations of the same stimuli during Phase 1. Both groups then received the same Phase 2 training consisting of simultaneous tone and light presentations paired with footshock. The Control group exhibited significant suppression of drinking to tone alone presentations after training, whereas the Blocking group did not. Metabolic mapping results demonstrated that blocking effects were localized to auditory regions receiving direct US somatosensory projections. Significantly greater C.O. activity in the inferior colliculus and the dorsal cochlear nucleus was found for the Blocking group relative to the Control group. Input cell layers of secondary auditory cortex also demonstrated a group difference, in that layers II/III and IV had lower levels of C.O. activity in the Blocking group. These specific changes in C.O. activity linked to behavioral training demonstrated that the blocking phenomenon produced distinct neural metabolic changes in CS processing in the auditory system localized to regions with CS-US interactions.
Previously it has been shown that the left hemisphere, but not the right, of split-brain patients tends to match the frequency of previous occurrences in probability-guessing paradigms (Wolford, Miller, & Gazzaniga, 2000). This phenomenon has been attributed to an "interpreter," a mechanism for making interpretations and forming hypotheses, thought to reside exclusively in the left hemisphere. In this study with a split-brain patient, we had him guess one of two types of faces, stimuli known to be preferentially processed in the right hemisphere of this patient. Unlike previous studies using other kinds of stimuli, the right hemisphere matched the frequency of the previous occurrences of a face-type, but the left hemisphere did not.
The involvement of monkey (Macaca fuscata) prefrontal cortex (PFC) neurons in motor output decisions was studied by recording single neuron activity during 3 tasks: (a) go-left, go-right, or no-go decisions, (b) operant bar press feeding based on discrimination of food and nonfood, and (c) either delayed matching-to-sample (DMS) or DMS with response delay. Combinations of single neuron responses during the 3 tasks suggested 7 types of PFC neurons that were related to attention, choice, task-unique memory, reward anticipation, laterality, initiation of movement, and suppression of movement. The authors suggest that responses of PFC neurons do not depend on physical properties of the stimuli, but on their behavioral significance. PFC neurons might be important for appropriate behavior in response to external stimuli and internal or motivational factors.
Two auditory discrimination tasks were thoroughly investigated: discrimination of frequency differences from a sinusoidal signal of 200 Hz and discrimination of differences in relative phase of mixed sinusoids of 200 Hz and 400 Hz. For each task psychometric functions were constructed for three observers, using nine different psychophysical measurement procedures. These procedures included yes-no, two-interval forced-choice, and various fixed- and variable-standard designs that investigators have used in recent years. The data showed wide ranges of apparent sensitivity. For frequency discrimination, models derived from signal detection theory for each psychophysical procedure seem to account for the performance differences. For phase discrimination the models do not account for the data. We conclude that for some discriminative continua the assumptions of signal detection theory are appropriate, and underlying sensitivity may be derived from raw data by appropriate transformations. For other continua the models of signal detection theory are probably inappropriate; we speculate that phase might be discriminable only on the basis of comparison or change and suggest some tests of our hypothesis.
Thirty patients with unilateral temporal lobe excisions and 15 normal control subjects were tested in a task involving judgements of timbre dissimilarity in single tone and melodic conditions. Perceptual correlates of spectral and temporal parameters resulting from changing the number of harmonics and rise-time duration, respectively, were investigated by using a multidimensional scaling technique. The results of subjects with left temporal lobe lesion suggest that they were able to use the spectral and temporal envelopes of tones independently in making perceptual judgements of single tones. In the melodic condition, their results were significantly different from those of normal control subjects, suggesting that left temporal lesions do affect subtle aspects of timbre perception, despite these patients' preserved ability to make discrimination judgements using traditional paradigms. The major finding of this study concerns perceptual ratings obtained by subjects with right temporal lobe lesion, which revealed a disturbed perceptual space in both conditions. The most distorted results were obtained with single tones, in which the temporal parameter was less prominent. Tones were grouped according to their spectral content, but the results did not reflect a coherent underlying perceptual dimension. In general, the data from both patient groups (left lesions and right lesions) showed that the extraction of temporal cues was easier in the melodic than in the single tone condition, suggesting that the different durations and frequencies heard in a musical phrase enhance the importance of certain physical parameters. The findings of the present study replicate and extend previous results showing that timbre perception depends mainly upon the integrity of right neocortical structures, although a contribution of left temporal regions is also apparent. These data also demonstrate that multidimensional techniques are sensitive to more subtle perceptual disturbances that may not be revealed by discrimination paradigms.
A battery of psychophysic tests has been designed through a computerized command of the patient's emitter. Because of the fatigability of these implanted patients, especially in the case of deaf-mute children, and the tedious aspect of these exams only 4 tests are commonly used: the threshold level in a Békésy way, the tone decay test, the 2 channels discrimination at different intensity levels, the lowest intensity discrimination. If the electrode impedances have been per-operatively measured, these tests are useful to understand the particular phonemic discrimination difficulties of each patient.
Frequency difference limens for pure tones preceded by a forward masker or followed by a backward masker were obtained across a wide range of signal levels. Relkin and Doucet [Hear. Res. 55, 215-222 (1991)] have shown that at a masker-signal delay of 100 ms, the thresholds of high-SR (spontaneous rate) auditory-nerve fibers are recovered, while the low-SR fiber thresholds are not. Therefore, forward-masked frequency discrimination potentially offers a method to investigate the role of low-SR fibers in the coding of frequency. It has been shown that when an intense forward masker is presented 100 ms before a pure-tone signal, intensity difference limens are elevated for mid-level signals [Zeng et al., Hear. Res. 55, 223-230 (1991)]. However, Plack and Viemeister [J. Acoust. Soc. Am. 92, 3097-3101 (1992)] have shown that a similar elevation in the intensity difference limen is obtained under conditions of backward masking, where selective adaptation of the auditory neurons would not be expected to occur. A condition of backward-masked frequency discrimination was therefore included to investigate the role of interference resulting from adding additional stimuli to a discrimination task. For signals at 1000 and 6000 Hz, there was no effect of a forward masker upon frequency difference limens. For the backward-masked conditions, an elevation of the frequency difference limen was observed at all signal levels, demonstrating that the effects of forward and backward maskers upon frequency discrimination are dissimilar and suggesting that cognitive effects are present in backward-masked discrimination tasks.(ABSTRACT TRUNCATED AT 250 WORDS)